Convert Antenna Height in Blue Book *27* Records from Height of ARP to Height of L1 Phase Center

This utility is designed to be used with Blue Book B-files produced by program CR8BB version 6.0 and above which contain Antenna Reference Point (ARP) heights. These files almost conform to the format of the *27* record in Chapter 2 of the Blue Book standard. However, if the user entered ARP heights (placed by the program in columns 56-60), these must be converted to L1-Phase-Center heights placed in columns 25-29. This utility fixes that problem by applying the following logic:

1. Each *27* record in the input B-File is examined. If CC 25-29 are non-blank, the program moves to the next record.If CC 25-29 are blank and CC 56-60 contain a number, then
2. The Job-Specific Antenna Number (JSAN) for this GPS Occupation is retrieved from the corresponding *25* record.
3. The B-File is searched for a *72* record for this JSAN. If it is not found, an error condition exists; see 5 below. If the *72* record is found, the NGS Antenna Code is retrieved.
4. The NGS file of antenna calibration constants is searched for this Antenna Code. If it is not found, an warning condition exists; see 6 below. If it is found, the ARP-to-L1 offset is retrieved and added to the the height of ARP from CC 56-60 of the *27* record. The resulting height of L1 phase center is written in CC 25-29.
5. (Error condition) Each time a *72* record is missing in step 3, the program compiles such occurrence. A list is returned to the user for input file correction; no heights are converted. Any warnings about a missing Antenna Code occurring in step 4 are also written to the list.
6. (Warning condition) If all *72* records are found but one or more antenna codes are missing, the program runs to completion, converting the heights; it lists the missing codes in a file with the recommendation that the user contact NGS and request that the antenna(s) be tested.
7. The updated B-File is returned to the user. The user may then use the browser's "Save Page As" function or cut and paste functions to save the updated B-File to the local computer.